Manufacturing method of secondary batteries

Abstract

This invention provides a manufacturing method that allows for accurate calculation of battery capacity in a short amount of time. [Solution] The manufacturing method disclosed herein includes a section capacity measurement step in which a battery assembly is charged to a predetermined upper limit SOC, then discharged to a lower limit SOC between 15% and 50%, and the section discharge capacity is measured; a self-discharge step in which the battery assembly is left for a predetermined period of time and the voltage of the battery assembly is measured; and a capacity calculation step in which the battery capacity of the battery assembly at SOC 0% to 100% is calculated. In the self-discharge step, the voltage of the battery assembly progresses through a voltage rise stage, a voltage stabilization stage, and a voltage drop stage, and the voltage value is obtained at least once in the voltage drop stage to be used as the post-discharge voltage. In the capacity calculation step, an estimated voltage V1 (or V2) at the completion of discharge is determined based on the post-discharge voltage, and the battery capacity is calculated by considering the section discharge capacity as the capacity up to the estimated voltage.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a secondary battery.

Background Art

[0002] In the manufacture of a typical secondary battery, after constructing a battery assembly by housing an electrode body and a non-aqueous electrolyte in a case, initial charging (conditioning), aging, and confirmation of performance before shipment (for example, confirmation of self-discharge amount, battery capacity, resistance, etc.) are performed.

[0003] For example, Patent Document 1 describes a method for manufacturing a secondary battery including a self-discharge step of leaving the battery assembly for a predetermined period to cause self-discharge after the aging step, and a capacity measurement step of measuring part or all of the battery capacity. Patent Document 1 describes, as an example, that in the capacity measurement step, after charging the battery assembly at a constant current until the state of charge SOC (State of charge) becomes 100%, discharging is performed at a constant current until SOC becomes 0%, and the amount of discharged electricity at this time is measured as the battery capacity.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] According to the study of the present inventor, the resistance becomes high in the region where the SOC is low. Therefore, when trying to discharge the battery assembly to SOC 0% during capacity measurement, the time required for discharging becomes long. On the other hand, if discharging is completed in a state where the SOC is high during capacity measurement, the overvoltage has a great influence on the voltage after discharge in addition to the open circuit voltage (OCV: Open Circuit Voltage), and there is a problem that the accuracy of capacity calculation deteriorates.

[0006] This invention has been made in view of the above circumstances, and aims to provide a method for manufacturing a secondary battery that can accurately calculate the battery capacity in a short amount of time. [Means for solving the problem]

[0007] The present invention discloses a method for manufacturing a secondary battery, comprising: a construction step of constructing a battery assembly by housing an electrode body and a non-aqueous electrolyte in a case; a section capacity measurement step of charging the battery assembly until the state of charge (SOC) reaches a predetermined upper limit of 65% or more, then discharging it until the state of charge (SOC) reaches a predetermined lower limit of 15% to 50%, and measuring the section discharge capacity in a predetermined discharge section; a self-discharge step of leaving the battery assembly for a predetermined period of time after the section capacity measurement step and measuring the voltage of the battery assembly; and a capacity calculation step of calculating the battery capacity of the battery assembly when the state of charge (SOC) is between 0% and 100% after the self-discharge step. In the self-discharge process described above, after the completion of discharge in the section capacity measurement process, the voltage of the battery assembly progresses through a voltage rise stage where it rises due to overvoltage, a voltage balance stage where the voltage rise due to overvoltage and the voltage drop due to self-discharge are in equilibrium, and a voltage drop stage where the voltage drops due to self-discharge. At least once in the voltage drop stage, the voltage value is obtained and set as the post-discharge voltage. In the capacity calculation process described above, the estimated voltage at the completion of discharge in the section capacity measurement process is determined based on the post-discharge voltage obtained in the self-discharge process, and the section discharge capacity measured in the section capacity measurement process is considered as the capacity up to the estimated voltage to calculate the battery capacity when the charge state of charge (SOC) is between 0 and 100%.

[0008] According to this invention, battery capacity can be calculated accurately in a short amount of time. Consequently, secondary batteries can be manufactured efficiently. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic longitudinal cross-sectional view of a secondary battery according to one embodiment. [Figure 2] Figure 2 is a flowchart of a manufacturing method according to one embodiment. [Figure 3] Figure 3 is a schematic graph showing the voltage change from the interval capacitance measurement process (process S4) to the self-discharge process (process S5). [Figure 4] Figure 4 is a partially enlarged view of the self-discharge process shown in Figure 3. [Figure 5] Figure 5 is a graph showing the change in voltage during a self-discharge process in one example. [Figure 6] Figure 6(A) is a graph relating to the comparative example, Figure 6(B) is a graph relating to Example 1, and Figure 6(C) is a graph relating to Example 2. [Modes for carrying out the invention]

[0010] Some preferred embodiments of the technology disclosed herein are described below. Matters other than those specifically mentioned herein but necessary for carrying out the technology disclosed herein (e.g., general configuration and manufacturing process of secondary batteries not characterizing the present invention) can be understood as design matters for those skilled in the art based on prior art. The present invention can be carried out based on the content disclosed herein and common technical knowledge in the art. Furthermore, in this specification, the notation "A to B" indicating a range encompasses not only the meaning of A or greater and B or less, but also the meanings of "greater than A" and "less than B".

[0011] [Secondary battery] First, the secondary battery disclosed herein will be described. In this specification, "secondary battery" is a term that refers to all energy storage devices that can be repeatedly charged and discharged, and is a concept that includes not only so-called secondary batteries such as lithium-ion secondary batteries, but also capacitors that utilize chemical reactions, such as lithium-ion capacitors and pseudocapacitance capacitors.

[0012] Figure 1 is a schematic longitudinal cross-sectional view of a secondary battery 100. As shown in Figure 1, the secondary battery 100 comprises a case 10, an electrode body 20, a positive electrode terminal 30, a negative electrode terminal 40, and a non-aqueous electrolyte (not shown). The secondary battery 100 is a non-aqueous electrolyte secondary battery in this case. The secondary battery 100 is preferably a lithium-ion secondary battery. The secondary battery 100 may also be a sodium-ion secondary battery.

[0013] Case 10 is a container for housing the electrode body 20 and a non-aqueous electrolyte. Case 10 comprises a case body 12 having an opening 12h and a sealing plate (lid) 14 that seals the opening 12h. Case 10 is integrated by joining the sealing plate 14 to the periphery of the opening 12h of the case body 12. Case 10 is airtightly sealed. The sealing plate 14 is provided with two terminal lead holes 18 and 19. The terminal lead holes 18 and 19 penetrate the sealing plate 14.

[0014] The positive terminal 30 is electrically connected to the positive tab 23 of the electrode body 20 via the positive current collector 50 inside the case 10. The positive terminal 30 extends from the inside to the outside of the case 10 through the terminal lead hole 18 of the sealing plate 14. The positive terminal 30 is located at one end of the sealing plate 14 (the left end in Figure 1). Here, the positive terminal 30 is crimped to the peripheral portion surrounding the terminal lead hole 18 of the sealing plate 14 by a crimping process.

[0015] The negative electrode terminal 40 is electrically connected to the negative electrode tab 25 of the electrode body 20 via the negative electrode current collector 60 inside the case 10. The negative electrode terminal 40 extends from the inside to the outside of the case 10 through the terminal lead-out hole 19 of the sealing plate 14. The negative electrode terminal 40 is located at the other end of the sealing plate 14 (the right end in Figure 1). Here, the negative electrode terminal 40 is crimped to the peripheral portion surrounding the terminal lead-out hole 19 of the sealing plate 14 by a crimping process.

[0016] The electrode body 20 is, here, a wound electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are laminated via a strip-shaped separator and wound around a winding axis. The electrode body 20 has a flat outer shape. The electrode body 20 is, here, arranged inside the case 10 with the winding axis along the lower surface 12a of the case 10. However, in other embodiments, the electrode body 20 may be arranged inside the case 10 with the winding axis along the side surface 12b of the case 10. Further, the electrode body 20 may be a laminated electrode body in which a plurality of rectangular (typically square) positive electrodes and a plurality of rectangular (typically square) negative electrodes are stacked in an insulated state. Also, the number of electrode bodies 20 arranged inside one case 10 may be one, or may be two or more (plural).

[0017] The configuration of the positive electrode is not particularly limited and may be the same as in the prior art. The positive electrode typically has a positive electrode current collector and a positive electrode active material layer fixed on at least one surface of the positive electrode current collector. A positive electrode tab 23 is attached to one end of the positive electrode current collector (the left end in FIG. 1) and is electrically connected to the positive electrode terminal 30 via the positive electrode current collecting member 50. The positive electrode active material layer contains a positive electrode active material. Examples of the positive electrode active material include lithium transition metal composite oxides such as lithium nickel cobalt manganese composite oxide.

[0018] The configuration of the negative electrode is not particularly limited and may be the same as in the prior art. The negative electrode typically has a negative electrode current collector and a negative electrode active material layer fixed on at least one surface of the negative electrode current collector. A negative electrode tab 25 is attached to the other end of the negative electrode current collector (the right end in FIG. 1) and is electrically connected to the negative electrode terminal 40 via the negative electrode current collecting member 60. The negative electrode active material layer contains a negative electrode active material. Examples of the negative electrode active material include carbon materials such as graphite and Si-containing materials containing silicon.

[0019] The non-aqueous electrolyte may be the same as the conventional one and is not particularly limited. The non-aqueous electrolyte is typically a liquid non-aqueous electrolyte solution containing a non-aqueous solvent (organic solvent) and a supporting salt (electrolyte salt). As an example of the non-aqueous solvent, cyclic carbonates such as ethylene carbonate (EC) and monofluoroethylene carbonate (FEC), and chain carbonates such as dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) can be mentioned. As an example of the supporting salt, lithium salts such as lithium hexafluorophosphate (LiPF6) and sodium salts can be mentioned. The non-aqueous electrolyte may further contain additives such as a film-forming agent. In other embodiments, the non-aqueous electrolyte may be solid or gel-like.

[0020] [Method for manufacturing secondary battery 100] Figure 2 is a flowchart of the method for manufacturing the secondary battery 100. As shown in Figure 2, the manufacturing method of this embodiment includes the following steps: a construction step (step S1), an initial charging step (step S2), an aging step (step S3), an interval capacity measurement step (step S4), a self-discharge step (step S5), and a capacity calculation step (step S6) in this order. However, the initial charging step (step S2) and the aging step (step S3) are optional and can be partially or entirely omitted in other embodiments. Also, the manufacturing method of this embodiment may further include other steps at any stage. For example, between the aging step (step S3) and the interval capacity measurement step (step S4), a conventionally known inspection step for performance confirmation, such as an inspection step for IV resistance (internal resistance), may be included. Note that from the interval capacity measurement step (step S4) to the capacity calculation step (step S6), it can also be understood as an inspection method for the battery capacity of the secondary battery 100.

[0021] The construction step (step S1) is the step of constructing a battery assembly by housing the electrode body 20 and the non-aqueous electrolyte in the case 10. In this embodiment, this step includes the electrode body preparation step (step S1A), the electrode body housing step (step S1B), and the electrolyte injection step (step S1C) in this order. However, the order of the electrode body housing step (step S1B) and the electrolyte injection step (step S1C) is not particularly limited. Also, if the non-aqueous electrolyte is in solid form (solid electrolyte), the electrolyte injection step (step S1C) can usually be omitted because the solid electrolyte is integrated with the electrode body. Furthermore, this step may include other steps at any stage.

[0022] In the electrode preparation step (step S1A), the electrode body 20 is prepared. The electrode body 20 may be purchased commercially or manufactured in-house. In one example, a wound electrode body is manufactured by stacking a strip-shaped positive electrode and a strip-shaped negative electrode in an insulated state (for example, via a strip-shaped separator) and winding them together. The wound electrode body can be manufactured, for example, by using a conventionally known winding device to wind the strip-shaped positive electrode, the strip-shaped negative electrode, and the strip-shaped separator into a roll shape around a winding axis.

[0023] In the electrode housing process (process S1B), the electrode body 20 obtained above is housed in the case 10. In one example, the electrode body 20 is housed inside the case body 12 through the opening 12h of the case body 12. Next, the sealing plate 14 is welded to the periphery of the opening 12h of the case body 12 to integrate the case body 12 and the sealing plate 14.

[0024] In the electrolyte injection step (step S1C), a non-aqueous electrolyte is prepared and injected into the case 10. In one example, the prepared non-aqueous electrolyte is injected into the case 10 containing the electrode body 20 through an injection hole (not shown) in the sealing plate 14. The battery assembly is constructed in this manner. In this specification, "battery assembly" refers to the entire intermediate product including the case 10, electrode body 20, and non-aqueous electrolyte in the manufacture of the secondary battery 100, and its configuration is not particularly limited. For example, the injection hole in the sealing plate 14 may be present before or after sealing.

[0025] The initial charging step (step S2) is an optional step in which the battery assembly is charged at least once. This step can be carried out according to a known method. For example, an external power supply is connected between the positive electrode terminal 30 and the negative electrode terminal 40 of the battery assembly, and charging is performed with a constant current at a typical room temperature range (20°C ± 10°C) until a predetermined target voltage is reached between the terminals. The target voltage is not particularly limited as it depends on the type of active material and non-aqueous solvent used, but in one example, it is preferable to set the SOC to 15-80%, and more preferably to set the SOC to 20-50%. As another example, if the negative electrode active material is a carbon material, it is preferable to set the target voltage to approximately 2.5V or higher, preferably 3V or higher, for example, 3.5V or higher, or 4V or higher.

[0026] The charging rate can be, for example, around 0.1C to 2C. In this process, after reaching a predetermined target voltage, the voltage may be maintained at a constant voltage for a predetermined time. In other words, constant current-constant voltage (CC-CV) charging may be performed in this process. Furthermore, charging may be performed only once, or it may be repeated two or more times, for example, with a discharge in between. Note that "1C" refers to the current value that can charge the battery capacity (Ah) predicted from the theoretical capacity of the positive electrode active material in one hour.

[0027] In this embodiment, the liquid injection hole of the sealing plate 14 is open during initial charging. After the initial charging is completed (in other words, before the start of the aging process), the liquid injection hole is sealed with the sealing member. As a result, the case 10 is airtightly sealed.

[0028] The aging process (step S3) is an optional step in which the battery assembly is held (left) in a predetermined temperature environment for a predetermined aging period. This step can be carried out according to a known method. The aging temperature is preferably set within the range of 25 to 80°C. In some embodiments, the aging temperature is preferably 40°C or higher, and more preferably in the high temperature range of 50°C or higher.

[0029] The aging period may vary depending on factors such as the aging temperature, but it is preferably 5 hours or more, and more preferably 10 hours or more. From the viewpoint of efficiency, the aging period is preferably 120 hours or less, and more preferably 72 hours or less. During this process, the battery assembly preferably maintains the voltage reached during the initial charge, for example, a voltage at which the State of Charge (SOC) of the battery assembly is 60-100% is preferred, and a voltage at which it is 80-100% is more preferred.

[0030] Furthermore, if aging is performed in the high-temperature range described above, and the section capacity measurement process described later is performed in the room temperature range (20°C ± 10°C), the process may also include leaving the battery assembly to cool down to the room temperature range after the completion of the aging period (in other words, before the start of the section capacity measurement process).

[0031] The interval capacity measurement step (step S4) is a step in which the interval discharge capacity in a predetermined discharge interval (range of SOC) is measured. Specifically, the battery assembly is charged until the charge state SOC reaches a predetermined upper limit SOC, and then discharged until the charge state SOC reaches a predetermined lower limit SOC, and the interval discharge capacity in the predetermined discharge interval is measured. Here, "discharge interval" refers to the voltage range (width) from the start of discharge to the end of discharge. In other words, it is the range (width) from the upper limit SOC (or upper limit charging voltage) during charging to the lower limit SOC (or discharge termination voltage) during discharge. This step is typically performed in the room temperature range (20℃ ± 10℃).

[0032] Charging may be performed using constant current (CC) charging or constant current-constant voltage (CC-CV) charging. The upper limit of state of charge (SOC) during charging should be 65% or higher (typically 65-100%) from the viewpoint of ensuring a wide discharge interval. In some embodiments, the upper limit of SOC is preferably 70% or higher, more preferably 80% or higher, and even more preferably 90-100%. In one example, the upper limit of SOC is 100%. This widens the discharge interval and can improve the measurement accuracy of the interval discharge capacity. Consequently, the calculation accuracy of the battery capacity in the capacity calculation process described later can be improved. The upper limit of SOC can be adjusted, for example, by setting the upper limit charging voltage during charging.

[0033] Discharge may be performed using constant current (CC) discharge or constant current-constant voltage (CC-CV) discharge. The lower limit of SOC during discharge is predetermined between 15% and 50%. According to the inventor's research, the resistance is high in the region where the lower limit of SOC is less than 15%, so attempting to discharge the battery assembly to the region below 15% results in a longer discharge time. By setting the lower limit of SOC to 15% or more, the time required for this process can be shortened, and the interval discharge capacity can be measured efficiently. Furthermore, by setting the lower limit of SOC to 50% or less, a discharge interval can be secured, and the measurement accuracy of the interval discharge capacity may be improved. Consequently, the calculation accuracy of the battery capacity in the capacity calculation process described later may be improved. In addition, if the negative electrode active material contains graphite, discharge can be advanced until the charging stage becomes Stage 2, which can particularly improve the measurement accuracy of the interval discharge capacity.

[0034] In some embodiments, the lower limit of SOC is preferably 40% or less, more preferably 30% or less, and even more preferably 25% or less. In one example, the lower limit of SOC is 16%. The discharge interval (upper limit SOC - lower limit SOC) is preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more, for example, 50-95% and 60-90% are even more preferred. This widens the discharge interval and can improve the measurement accuracy of the interval discharge capacity. Consequently, the calculation accuracy of the battery capacity in the capacity calculation process described later can be improved. The lower limit of SOC can be adjusted, for example, by setting the discharge termination voltage (cutoff voltage) during discharge.

[0035] As described above, in this process, the section discharge capacity in a predetermined discharge section is measured. The section discharge capacity is an actual measured value (Ah). For example, if the upper limit SOC is 100% and the lower limit SOC is 16%, the amount of discharged electricity in the discharge section from SOC 100% to 16% is measured as the section discharge capacity. In one example, the amount of discharged electricity when discharging with constant current (CC) down to the lower limit SOC can be used as the section discharge capacity. In another example, the amount of discharged electricity when discharging with constant current (CC) down to the lower limit SOC and then discharging with constant voltage (CV) can be used as the section discharge capacity. The measured section discharge capacity is converted to battery capacity (capacity from SOC 0 to 100%) in the capacity calculation process (process S6) described later, from the perspective of performance verification before shipment.

[0036] The self-discharge process (process S5) is a process in which, after the completion of the interval capacity measurement process (more specifically, after the discharge in the interval capacity measurement process is completed), the battery assembly is left for a predetermined period of time and the voltage of the battery assembly is measured. This process is typically carried out in the room temperature range (20℃ ± 10℃). However, the ambient temperature can be changed from the room temperature range at some or all of the stages described later.

[0037] Figure 3 is a schematic graph showing the voltage transition from the interval capacity measurement process (process S4) to the main process (process S5). Figure 4 is a magnified view of the main process from the graph in Figure 3, and is a schematic graph showing the voltage transition in the main process. According to the inventor's research, as shown in Figure 4, in the main process, after the discharge in the interval capacity measurement process is completed, the voltage of the battery assembly transitions in the following order: voltage rise stage (phase 1), voltage stabilization stage (phase 2), and voltage drop stage (phase 3).

[0038] The voltage rise stage (Phase 1), as shown in Figure 4, is a stage where voltage mitigation due to overvoltage plays a significant role. In other words, it is a stage where the voltage rise due to overvoltage is greater than the voltage drop due to self-discharge (overvoltage > self-discharge). Therefore, in Phase 1, the voltage rises due to overvoltage from the voltage at the completion of discharge in the section capacity measurement process (Process S4) (the slope of the graph representing the voltage change becomes positive). The effect of overvoltage decreases over time. And the slope of the graph representing the voltage change becomes gentler after passing the maximum point.

[0039] In some embodiments, it is preferable to maintain the battery assembly at a high temperature of 50°C or higher for at least a portion of the voltage rise stage (phase 1). This makes it easier to reduce the effects of overvoltage in a short time, thus shortening the time the voltage remains in phase 1 (for example, within 40 hours, or even within 30 hours). Therefore, it becomes easier to move to the next stage (phase 2) earlier. Consequently, the secondary battery 100 can be manufactured efficiently. If a portion of this stage (the preceding part) is performed in the high temperature range described above, and the voltage balancing stage (phase 2), described later, is performed in the room temperature range (20°C ± 10°C), it is preferable to cool the battery assembly to the room temperature range before the start of the voltage balancing stage (in other words, in the later part of this process).

[0040] The voltage balancing stage (Phase 2), as shown in Figure 4, is the stage where the voltage increase due to overvoltage and the voltage decrease due to self-discharge are in equilibrium (overvoltage ≈ self-discharge). Therefore, in Phase 2, the slope of the graph representing the voltage change approaches 0. In reality, as the effect of overvoltage decreases over time, as shown in Figure 4, the voltage decrease due to self-discharge is often slightly greater than the voltage increase due to overvoltage, and the slope of the graph representing the voltage change is often slightly negative. If the entire voltage rise stage (Phase 1) is performed in the high-temperature range as described above, and the voltage drop stage (Phase 3), which will be described later, is performed in the room temperature range (20°C ± 10°C), it is preferable to cool the battery assembly to the room temperature range after the completion of the voltage rise stage and before the start of the voltage drop stage (in other words, during this process).

[0041] The voltage drop stage (Phase 3), as shown in Figure 4, is the stage where the effect of overvoltage becomes sufficiently small and the voltage drop due to self-discharge becomes dominant (overvoltage < self-discharge). Therefore, in Phase 3, the voltage drops due to self-discharge (the slope of the graph representing the voltage change becomes negative). The voltage typically changes at a constant slope over time.

[0042] In some embodiments, it is preferable to keep the battery assembly at room temperature of 20°C ± 10°C during the voltage drop stage (phase 3). This improves the accuracy of voltage measurement, and consequently, the accuracy of battery capacity calculation in the capacity calculation process described later.

[0043] As described above, in this process, the voltage value is acquired at least once during the voltage drop stage (phase 3), and the acquired voltage value is taken as the post-discharge voltage. Since this post-discharge voltage is the voltage value during the voltage drop stage, it can be said that the effects of overvoltage have been sufficiently reduced (eliminated), as described above. Voltage measurements may be performed continuously or intermittently at predetermined intervals during the self-discharge process (process S5) or during the voltage drop stage (phase 3), or at only one or more predetermined points within the voltage drop stage (phase 3).

[0044] The time it takes to transition from the discharge in the preceding interval capacity measurement process (process S4) through the voltage rise stage (phase 1) and the voltage stabilization stage (phase 2) to the voltage drop stage (phase 3) can vary depending on, for example, the battery configuration and the charge / discharge conditions in the interval capacity measurement process (process S4) (e.g., upper limit SOC and lower limit SOC). Therefore, when mass-producing the secondary battery 100, it is preferable to conduct preliminary tests to confirm the time required for each stage in advance. If the time required to transition to the voltage drop stage (phase 3) has been confirmed, then it is sufficient to measure the voltage only during a predetermined time within the voltage drop stage (phase 3).

[0045] In some embodiments, it is preferable to obtain the post-discharge voltage at least 50 hours after the completion of the interval capacity measurement process (more specifically, after the discharge in the interval capacity measurement process is completed). For example, the post-discharge voltage is obtained at least 100 hours after the completion of the interval capacity measurement process. This can sufficiently reduce the effect of overvoltage and improve the accuracy of battery capacity calculation in the capacity calculation process described later. On the other hand, if the time between the completion of the interval capacity measurement process and the acquisition of the post-discharge voltage is too long, the effect of self-discharge may become too large. Therefore, in some embodiments, it is preferable to obtain the post-discharge voltage within 150 hours after the completion of the interval capacity measurement process and the transition to the voltage drop stage (phase 3), and more preferably within 120 hours or 110 hours.

[0046] In some embodiments, it is preferable to acquire the post-discharge voltage multiple times during the voltage drop stage (phase 3). As will be explained in detail in the section on the capacity calculation process, this reduces the effect of voltage drop due to self-discharge, even if the time from the completion of the interval capacity measurement process (more specifically, after the discharge in the interval capacity measurement process is completed) until the post-discharge voltage is acquired, thereby potentially improving the accuracy of battery capacity calculation.

[0047] When acquiring the post-discharge voltage multiple times, it is preferable to stagger the timing of acquiring the post-discharge voltages to some extent. Although not particularly limited, in some embodiments, it is preferable to leave at least 24 hours between acquiring the first post-discharge voltage value and acquiring the second post-discharge voltage value. This can improve the accuracy of the correction in the capacity calculation process described later, and potentially improve the accuracy of the battery capacity calculation.

[0048] This process can be terminated after obtaining the discharge voltage once or multiple times. While not particularly limited, the total time required for this process can typically be set to 50 hours or more, for example, 100 hours or more, from the viewpoint of sufficiently reducing the effects of overvoltage. Alternatively, the total time required for this process can typically be set to 200 hours or less, for example, 150 hours or less, from the viewpoint of preventing the effects of self-discharge from becoming too large and from the viewpoint of productivity.

[0049] The capacity calculation step (step S6) is a step that calculates the battery capacity of the battery assembly when the state of charge (SOC) is between 0% and 100% after the self-discharge step. Specifically, it is a step that first determines the estimated voltage at the end of discharge in the interval capacity measurement step (step S4) based on the post-discharge voltage obtained in the self-discharge step (step S5), and then calculates the battery capacity when the SOC is between 0% and 100% by considering the interval discharge capacity measured in the interval capacity measurement step (step S4) as the capacity up to the estimated voltage. The estimated voltage is based on the post-discharge voltage, which has reduced the effect of overvoltage, and is therefore a value in which the effect of overvoltage has been sufficiently reduced. Therefore, when converting to the battery capacity at SOC 0-100%, by considering the interval discharge capacity in a predetermined discharge interval as the capacity up to the estimated voltage, errors due to overvoltage can be reduced and the battery capacity can be calculated with high accuracy.

[0050] In the first embodiment, as shown by the symbol V1 in Figure 3, the post-discharge voltage obtained in the self-discharge process (process S5) is considered as the estimated voltage, and the battery capacity is calculated by directly determining a coefficient from the estimated voltage (post-discharge voltage). More specifically, a capacity conversion formula is created by multivariate analysis with the battery capacity as the dependent variable and the interval discharge capacity measured in the interval capacity measurement process (process S4) and the estimated voltage (post-discharge voltage obtained in the self-discharge process) as independent variables, and the battery capacity is calculated. This allows for the simple calculation of battery capacity.

[0051] In one example of multivariate analysis, the battery capacity is used as the dependent variable, and the interval discharge capacity and estimated voltage (post-discharge voltage) are used as independent variables. Multiple regression analysis is performed to calculate the battery capacity using the following equation: Battery Capacity = a × Interval Discharge Capacity + b × Estimated Voltage + c (where a is the coefficient of interval discharge capacity, b is the coefficient of estimated voltage, and c is the intercept). The above a and b are typically positive real numbers. In one specific example, a is 1.16058, b is 402.2097, and c is -1386.6. However, the above equation is merely an example and is not limited to it. In the technology disclosed herein, the capacity conversion formula can be selected from, for example, higher-order polynomials, exponential functions, logarithmic functions, powers, etc.

[0052] In a second (alternative) embodiment, the process includes a first step of estimating the post-discharge state of charge (SOC) and a second step of calculating the battery capacity using the estimated post-discharge SOC. In the first step, as shown by the symbol V1 in Figure 3, the post-discharge voltage obtained in the self-discharge process (step S5) is considered as the estimated voltage, and based on the relationship formula between voltage and charge state SOC, the post-discharge SOC, which represents the charge state at the completion of discharge in the interval capacity measurement process (step S4), is estimated from the estimated voltage (post-discharge voltage). The relationship formula between voltage and charge state SOC (the so-called SOC-OCV curve) may differ depending on the battery configuration (e.g., positive electrode, negative electrode, non-aqueous electrolyte components, etc.) and is predetermined by preliminary tests, etc.

[0053] In the second step, the battery capacity (Ah) is calculated by considering the interval discharge capacity (Ah) measured in the interval capacity measurement step (step S4) as the capacity from the upper limit SOC to the post-discharge SOC. Specifically, the interval discharge capacity measured in the interval capacity measurement step (step S4), the upper limit SOC in the interval capacity measurement step (step S4), and the post-discharge SOC estimated in the first step are used in the following equation (1):

number

[0054] Furthermore, if multiple post-discharge voltages are obtained in the voltage drop stage (phase 3), a preliminary step to calculate the estimated voltage is included before the first step. In the preliminary step, for example, as shown by the dotted line in Figure 3, a graph representing the voltage change is created with the elapsed time from the completion of discharge in the interval capacity measurement step on the X axis and the voltage (which may be the amount of voltage change) on the Y axis, and the equation of the straight line passing through the first post-discharge voltage and the second post-discharge voltage (y=ax+b) is determined. There may be two or more post-discharge voltage values. Then, as shown by the symbol V2 in Figure 3, the intercept c of the obtained straight line (in other words, the intersection point of the obtained straight line and the straight line Y=0) is considered as the estimated voltage (voltage at the completion of discharge in the interval capacity measurement step (step S4)). Then, it is preferable to calculate the battery capacity by correcting the interval discharge capacity according to the first and second steps in the second embodiment described above. This reduces the effect of self-discharge in addition to the effect of overvoltage described above, so the estimation accuracy of the post-discharge SOC can be further improved. This could potentially lead to further improvements in the accuracy of battery capacity calculations.

[0055] As described above, the secondary battery 100 can be suitably manufactured. Normally, when the secondary battery 100 is shipped, the state of charge (SOC) is around 20%. Therefore, after the self-discharge process (or capacity calculation process), a process of charging the battery assembly may or may not be included, for example, when shipping the secondary battery 100. In some embodiments, the process of charging the battery assembly after the self-discharge process (or capacity calculation process) is not included. In the technology disclosed herein, since the discharge is performed in the self-discharge process so that the state of charge (SOC) is between 15% and 50%, it is possible to omit charging for shipping. This improves the productivity of the secondary battery 100.

[0056] <Applications of the 100-cell rechargeable battery> The secondary battery 100 can be used for various purposes, but it is particularly suitable for use as a power source (driving power supply) for motors mounted on vehicles such as passenger cars and trucks. The type of vehicle is not particularly limited, but examples include plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), and battery electric vehicles (BEVs).

[0057] The following describes some embodiments of the present invention, but it is not intended to limit the present invention to these embodiments.

[0058] In this test example, the transition time to the voltage drop stage (phase 3) in the self-discharge process (process S5) was first confirmed. Figure 5 is a graph showing the change in voltage during the self-discharge process in one example. In this example, as indicated by the symbol P0 in Figure 5, it was confirmed that the effects of overvoltage were sufficiently reduced and the system transitioned to the voltage drop stage (phase 3) 50 hours after the completion of the discharge in the section capacity measurement process (process S4).

[0059] In this test example, the section discharge capacity was measured in the section capacity measurement process, with the upper limit SOC set to 100% and the lower limit SOC to 16%. The accuracy of the battery capacity calculation was then compared when the value of "SOC after discharge" in the above formula (1) used in the capacity calculation process (process S6) was changed. Specifically, In the comparative example, the "SOC after discharge" was estimated from the measured voltage at the completion of discharge in the interval capacity measurement process (process S4), based on a predetermined relationship formula between voltage and charge state (SOC); In Example 1, one post-discharge voltage is obtained during the voltage drop stage (position indicated by symbol P1 in Figure 5) in the self-discharge process (process S5), and this obtained post-discharge voltage V1 is considered as the estimated voltage. Based on a predetermined relationship between voltage and charge state (SOC), the "post-discharge SOC" is estimated from the estimated voltage; In Example 2, multiple post-discharge voltages are acquired during the voltage drop phase (positions P1 and P2 in Figure 5) of the self-discharge process (process S5). A straight line passing through these acquired post-discharge voltages is determined, and the intercept of this line is considered the estimated voltage. Based on a predetermined relationship between voltage and charge state (SOC), the "post-discharge SOC" is estimated from the estimated voltage; Each approximation curve is obtained based on multiple test results, and the accuracy (R) is calculated. 2 The values ​​were compared.

[0060] Figure 6(A) is a graph relating to the comparative example, Figure 6(B) is a graph relating to Example 1, and Figure 6(C) is a graph relating to Example 2. The vertical axis (cell capacity) of each graph represents the discharge capacity (the inherent capacity of the battery) when discharged from SOC 100% to SOC 0%, and the horizontal axis (battery capacity) represents the battery capacity calculated by the above formula (1). As shown in Figure 6(A), in the comparative example, R 2 The value was approximately 0.51, indicating the lowest accuracy. This is likely because, in addition to OCV, overvoltage significantly affects the voltage at the end of discharge, and the battery resistance negatively impacted the accuracy.

[0061] In contrast, as shown in Figure 6(B), in Example 1, where the interval discharge capacity is corrected based on a single post-discharge voltage obtained during the voltage drop phase, R 2The value was approximately 0.64, indicating a significant improvement in calculation accuracy. This is likely because allowing a period of time (more than 50 hours in this case) after the discharge was completed during the interval capacity measurement process sufficiently reduced the effects of overvoltage. Furthermore, as shown in Figure 6(C), in Example 2, where the interval discharge capacity was corrected based on multiple post-discharge voltages acquired during the voltage drop phase, R 2 The value was approximately 0.72, indicating a further improvement in calculation accuracy. This is likely due to the reduction in the effects of overvoltage, as well as the reduction in the effects of voltage drop due to self-discharge. These results demonstrate the significance of the technology disclosed herein.

[0062] Although several embodiments of the present invention have been described above, these embodiments are merely examples. The present invention can be implemented in various other forms.

[0063] As described above, specific embodiments of the technology disclosed herein include those described in the following sections. Item 1: A construction step of constructing a battery assembly by housing an electrode body and a non-aqueous electrolyte in a case; a section capacity measurement step of charging the battery assembly until the charge state (SOC) reaches a predetermined upper limit SOC of 65% or more, then discharging it until the charge state (SOC) reaches a predetermined lower limit SOC between 15% and 50%, and measuring the section discharge capacity in a predetermined discharge section; a self-discharge step of leaving the battery assembly for a predetermined period after the section capacity measurement step and measuring the voltage of the battery assembly; and a capacity calculation step of calculating the battery capacity of the battery assembly when the charge state (SOC) is between 0% and 100% after the self-discharge step. In the self-discharge process described above, after the completion of discharge in the section capacity measurement process, the voltage of the battery assembly progresses through a voltage rise stage in which it rises due to overvoltage, a voltage balancing stage in which the voltage rise due to overvoltage and the voltage drop due to self-discharge are in equilibrium, and a voltage drop stage in which the voltage drops due to self-discharge. At least once in the voltage drop stage, the voltage value is obtained and set as the post-discharge voltage. A method for manufacturing a secondary battery, comprising the following steps: in the capacity calculation step, the estimated voltage at the completion of discharge in the section capacity measurement step is determined based on the post-discharge voltage obtained in the self-discharge step, and the section discharge capacity measured in the section capacity measurement step is considered as the capacity up to the estimated voltage to calculate the battery capacity when the charge state of charge (SOC) is between 0 and 100%. Item 2: The manufacturing method described in Item 1, wherein in the capacity calculation step, the post-discharge voltage is considered as the estimated voltage, the battery capacity is used as the dependent variable, and a capacity conversion formula is created by multivariate analysis using the interval discharge capacity and the estimated voltage as independent variables, and the battery capacity is calculated. Section 3: In the capacity calculation step described above, the post-discharge voltage is considered to be the estimated voltage, and based on a predetermined relationship formula between the battery voltage and the charge state (SOC), the post-discharge SOC, which represents the charge state at the completion of discharge in the section capacity measurement step described above, is estimated from the estimated voltage, and the section discharge capacity, the upper limit SOC, and the post-discharge SOC are used in the following equation (1):

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[0064] 10 cases 20 Electrode body 100 Secondary battery S1 construction process S4 Section Capacity Measurement Process S5 Self-discharge process S6 Capacity calculation process

Claims

1. A construction process involves housing the electrode body and non-aqueous electrolyte in a case to construct a battery assembly, The battery assembly is charged until its state of charge (SOC) reaches a predetermined upper limit of 65% or more, and then discharged until its state of charge (SOC) reaches a predetermined lower limit of 15% to 50%, and the interval discharge capacity in a predetermined discharge interval is measured. After the section capacity measurement step, a self-discharge step is performed in which the battery assembly is left for a predetermined period of time and the voltage of the battery assembly is measured. After the self-discharge step, a capacity calculation step is performed to calculate the battery capacity when the charge state (SOC) of the battery assembly is between 0 and 100%. Includes, In the self-discharge process, After the discharge in the aforementioned section capacity measurement step is completed, the voltage of the battery assembly progresses through a voltage rise stage in which it rises due to overvoltage, a voltage balancing stage in which the voltage rise due to overvoltage and the voltage drop due to self-discharge are in equilibrium, and a voltage drop stage in which the voltage drops due to self-discharge. During the voltage drop phase, the voltage value is obtained at least once and used as the post-discharge voltage. In the aforementioned capacity calculation process, Based on the post-discharge voltage obtained in the self-discharge step, the estimated voltage at the completion of discharge in the section capacity measurement step is determined. The section discharge capacity measured in the section capacity measurement step is considered as the capacity up to the estimated voltage, and the battery capacity at a charge state of charge (SOC) of 0 to 100% is calculated. A method for manufacturing secondary batteries.

2. In the aforementioned capacity calculation process, The voltage after discharge is considered to be the estimated voltage, A multivariate analysis is performed using the aforementioned battery capacity as the dependent variable, and the aforementioned interval discharge capacity and the aforementioned estimated voltage as independent variables to create a capacity conversion formula and calculate the aforementioned battery capacity. The manufacturing method according to claim 1.

3. In the aforementioned capacity calculation process, The voltage after discharge is considered to be the estimated voltage, Based on a predetermined relationship between voltage and charge state SOC, the post-discharge SOC, which represents the charge state at the completion of discharge in the section capacity measurement process, is estimated from the estimated voltage. Using the aforementioned section discharge capacity, the aforementioned upper limit SOC, and the aforementioned post-discharge SOC, the following equation (1): [Math 1] From this, the battery capacity is calculated when the charge state (SOC) is between 0 and 100%. The manufacturing method according to claim 1.

4. In the self-discharge process, the post-discharge voltage is acquired multiple times during the voltage drop stage. In the aforementioned capacity calculation process, In the section capacity measurement process, a graph is created with the elapsed time from the completion of discharge on the X axis and the voltage on the Y axis. A straight line is found that passes through the first post-discharge voltage and the second post-discharge voltage, and the intercept of the straight line is considered to be the estimated voltage. Based on a predetermined relationship between voltage and charge state SOC, the post-discharge SOC, which represents the charge state at the completion of discharge in the section capacity measurement process, is estimated from the estimated voltage. Using the aforementioned section discharge capacity, the aforementioned upper limit SOC, and the aforementioned post-discharge SOC, the following equation (1): [Math 2] From this, the battery capacity is calculated when the charge state (SOC) is between 0 and 100%. The manufacturing method according to claim 1.

5. In the self-discharge process, there is a gap of at least 24 hours between obtaining the first post-discharge voltage value and obtaining the second post-discharge voltage value. The manufacturing method according to claim 4.

6. In the self-discharge step, the post-discharge voltage is acquired at least 50 hours after the completion of the section capacity measurement step. The manufacturing method according to any one of claims 1 to 4.

7. In the self-discharge step, the battery assembly is held at a high temperature of 50°C or higher for at least a portion of the voltage rise step. The manufacturing method according to any one of claims 1 to 4.

8. In the self-discharge process, the battery assembly is kept at a room temperature of 20°C ± 10°C during the voltage drop stage. The manufacturing method according to claim 7.

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